1. Field of the Invention
The present invention relates to a smart antenna device with improved reception quality obtained by adjusting a phase shift for signals received in a plurality of antennas and by weighting the signals, and a complex smart antenna device using a plurality of smart antenna devices.
2. Description of the Related Art
A smart antenna technique (or sometimes called as an adapting antenna technique) is a technique to adjust a phase shift for signals received in a plurality of antennas and weight the signals so as to maximize the S/N (signal-to-noise ratio) after the signals are added to each other. FIG. 7 shows a basic configuration of an adapting antenna device using such a technique.
In FIG. 7, reference numerals A1 to Ak denote antenna elements, reference numerals B1 to Bk denote A/D converters for performing an analog/digital conversion for signals received in the antenna elements A1 to Ak, reference numerals C1 to Ck denote a weighting part for multiplying the signals X(n) converted into digital signals by the A/D converters B1 to Bk by respective weights W1 to Wk, reference numeral 1 denotes an adder for adding results of the multiplication of the weighting parts C1 to Ck to output an output signal Y(n), and reference numeral 2 denotes a signal processing part that obtains an evaluation function Q(n) for evaluating distortion of amplitudes of the received signals X(n) from the output signal Y(n) output from the adder 1 and its envelope value s and updates the weights W(n) of the antenna elements A1 and Ak on the basis of the evaluation function Q(n).
First, the output signal Y(n) output from the adder 1 and the envelope value s are put in the calculation equation Q(n)=(||Y(n)|p−sp|q) (where, p and q are integers of 1 or 2) to obtain the evaluation function Q(n) for evaluating the distortion of the amplitudes of the received signals X(n).
After obtaining the evaluation function Q(n), the signal processing part 2 updates the weights W(n) of the received signals X(n) on the basis of the obtained evaluation Q(n) in order to minimize distortion of the received signals X(n). Specifically, the evaluation function Q(n) is partially differentiated with respect to a weight W(n), and a next weight W(n+1) is determined by using a result of the partial differentiation ∇wQ(n), according to the following equation.W(n+1)=W(n)−μ·∇wQ(n)
Here, μ is a step size (a step width of evaluation).
The weight W(n) is a vector representing weights W1 to Wk at time n, and has normalized integers at an initial stage, as set in a manner that W1=1, W2=0, W3=0, . . . , Wk=0.
Then, the weighting parts C1 to Ck weight the received signals X(n) by using the determined weight W(n+1) in order to minimize distortion of amplitudes of the received signals X(n). In addition, even if an interference wave having low power is derived from a desired signal wave, the interference wave is suppressed (for example, see JP-A-11-284423 (FIG. 5)).
In the conventional signal receiving unit, the weight W(n) to minimize the distortion of the amplitudes of the received signals X(n) is gradually updated, however, a weight W(1) at the initial stage is set as a normalized integer, so that a problem arises in that it takes a long time to obtain optimal weights W(n). In addition, since a weight operation is performed after digital conversion, a problem occurs where even more process time is required.